1. Field of the Invention
The present invention relates generally to a reception apparatus and method in a Broadband Wireless Access (BWA) communication system, and in particular, to an apparatus and method for processing data in a modem for a Mobile Station (MS) used in a Wireless Broadband Internet (Wibro) system.
2. Description of the Related Art
Technology generally used to provide a data service to users in the current wireless communication environment are classified into a 2.5th Generation (2.5G) or 3rd Generation (3G) cellular mobile communication technology, such as Code Division Multiple Access 2000 1x Evolution Data Optimized (CDMA2000 1xEVDO), General Packet Radio Services (GPRS) and Universal Mobile Telecommunication Service (UMTS), and a Wireless Local Area Network (LAN) technology, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 Wireless LAN, and HiperLAN/2.
The most noticeable characteristic of the 3G cellular mobile communication technology for providing voice services over the circuit-based network is to provide packet data services in which subscribers can access the Internet in the broadband wireless communication environment.
However, the cellular mobile communication network is limited in its support of the high-speed packet data services. For example, the CDMA2000 1xEVDO system, a synchronous mobile communication system, supports a data rate of up to about 2.4 Mbps.
Aside from the evolution of the mobile communication technologies, various local wireless access technologies such as IEEE 802.16-based Wireless LAN, HiperLAN/2 and Bluetooth have appeared. However, such technologies cannot guarantee the mobility level being equivalent to that of the cellular mobile communication system. Nevertheless, the local wireless access technologies are presented as an alternative for providing high-speed data services in the wireless environment, replacing the wire communication networks such as a cable modem and Digital Subscriber Line (DSL), in a Hot Spot zone such as a public space and school, or in the home network environment.
However, the Wireless LAN, providing the high-speed data services, is limited in providing public network services to users not only due to highly limited mobility and narrow coverage area but also due to radio interference.
Therefore, various attempts are being made to overcome the limitations. For example, extensive research is being conducted on the Portable Internet technology proposed to make the best use of the cellular mobile communication system and the Wireless LAN. Particularly, active research is being conducted on the Wireless Broadband Internet (Wibro) system, which is a typical example of the Portable Internet technology now under standardization and development. The Wibro system can provide high-speed data services in the indoor/outdoor stationary environments and the pedestrian-speed and mid/low-speed (about 60 Km/h) mobile environment, using various types of mobile stations. A detailed description will now be made of the Wibro system.
The Wibro system, a technology evolved one step from the 2.3-GHz band Wireless Local Loop (WLL) technology, covers the 4th Generation (4G) mobile communication industry field, and can cover the wider industry field compared to 3G IMT-2000. Therefore, Wibro is also referred to as a 3.5th Generation (3.5G) mobile communication technology.
To provide a Wibro service with application of Wibro technology, the system and Mobile Station (MS) corresponding thereto are now under active development. There is no specific standard on a modem for the Wibro mobile station. For convenience, the Wibro-based broadband wireless communication system will also be referred to herein as a broadband wireless communication system.
FIG. 1 illustrates a Wibro data frame format used in the general broadband wireless communication system.
Shown in FIG. 1 is a data frame format based on the 802.16e standard for providing a broadband wireless communication service such as the Wibro service, and the Wibro data frame used in the Wibro communication system is time-divided into a Downlink (DL) region and an Uplink (UL) region. In the downlink-to-uplink transition interval, a Transmit/receive Transition Gap (TTG) forms a guard time, and in the uplink-to-downlink transition interval, a Receive/transmit Transition Gap (RTG) forms a guard time. In FIG. 1, the horizontal axis indicates Orthogonal Frequency Division Multiple Access (OFDMA) symbol numbers, and the vertical axis indicates subchannel logical numbers.
As to the downlink, a preamble for synchronization acquisition is disposed in a Kth OFDMA symbol, and broadcast data information to be commonly received by mobile stations, such as a Frame Control Header (FCH) and a DownLink MAP (DL-MAP), is disposed in a (K+1)th OFDMA symbol. The FCH, composed of two subchannels, delivers basic information on subchannel, ranging and modulation scheme. DownLink bursts (DL bursts), for example, DL burst#1 to DL burst#6, are disposed over (K+3)th to (K+15)th OFDMA symbols.
Next, as to the uplink, UpLink bursts (UL bursts) are disposed over (K+17)th to (K+26)th OFDMA symbols. Further, a ranging subchannel for ranging is disposed over the (K+17)th to (K+26)th OFDMA symbols.
In the Wibro data frame format used in the IEEE 802.16e communication system, the downlink frame, as described above, includes a preamble region, an FCH region, a DL-MAP region, a UL-MAP region, and multiple DL burst regions.
The preamble region is a region for transmitting a synchronization signal, or a preamble sequence, for synchronization acquisition between a transmitter, or a Base Station (BS), and a receiver, or a Mobile Station (MS). That is, the preamble region is needed to match synchronization with the data transmitted from the base station, and a modem of the mobile station extracts synchronization information from the preamble using several methods.
The FCH region, composed of 4 subchannels, delivers basic information on a DL-MAP, such as length and modulation scheme of the DL-MAP. For example, by analyzing the FCH information, the mobile station can determine a size of the DL-MAP, and also can determine which of Frequency Reuse Factors (hereinafter referred to as ‘reuse’), for example, reuse=1 and reuse=3, used in the base station is applied. The modulation scheme of the DL-MAP is changed on a frame-by-frame.
The DL-MAP region is a region for sending a DL-MAP message, and has a variety of information used for extracting information such as position and size of the data in the downlink frame, and providing a service to the mobile station. By analyzing the DL-MAP information, the mobile station can extract the data in the frame.
With use of the DL burst regions, the mobile station extracts the data based on the general data information, for example, the information acquired by analyzing the DL-MAP.
The subchannel described herein means a channel composed of multiple subcarriers, and a predetermined number of subcarriers constitute one subchannel according to system conditions. One frame is composed of several symbols, for example, 42 symbols in the Wibro system, and the symbols each can be divided into several subchannels. The symbol can be regarded as a unit in which the frame is divided in the time domain, and a data size in one symbol depends on the format of the frame.
The uplink frame in the Wibro data frame format used in the IEEE 802.16e communication system includes, as described above, multiple UL burst regions and the ranging subchannel region. The ranging subchannel region is a region over which ranging subchannels for ranging are transmitted, and by using the UL burst regions, the mobile station extracts data based on the general data information, for example, information acquired by analyzing the UL-MAP.
To extract data from the downlink regions of the Wibro data frame according to the 802.16e standard, the following data processing order is needed.
1) A process of analyzing reuse information in the FCH, and FCH information used for acquiring the DL-MAP size information.
2) A process of performing DL-MAP decoding to acquire a variety of information used for extracting normal bursts except for Hybrid Automatic ReQuest (HARQ) bursts depending on information in the DL-MAP. HARQ bursts and normal bursts can coexist in one frame, and data allocation in the frame can be changed on a frame-by-frame basis.
3) A process of extracting normal bursts based on the information acquired from the DL-MAP.
When the data processing process is performed in order of 1), 2) and 3), data reception for one frame is completed. Generally, a Wibro modem is a very important component in the data processing scheme, as a high data rate (for example, downlink 10 Mbps) is required and the data structure is complex like the Partial Usage Subchannel (PUSC), Full Usage SubChannel (FUSC), reuse factor, etc.
FIG. 2 illustrates a structure of a data processing apparatus in the general broadband wireless communication system.
Before a description of FIG. 2 is given, a structure of an 802.16e-based Wibro modem is roughly divided into a synchronization unit, a reception (Rx) data processing unit including a Convolutional Turbo Code (CTC) decoder and a Convolutional Code (CC) decoder, and a transmission (Tx) data processing unit including a Medium Access Control (MAC) entity, a CTC encoder and a CC encoder. In this Wibro modem structure, shown in FIG. 2 is a block structure for data decoding processing in the Rx data processing unit.
Shown in FIG. 2 is a block structure for data decoding processing in the conventional Rx data processing unit, and the block structure includes a channel estimator 210, a decoder 230, and a MAP decoder 250.
The channel estimator 210 estimates channels based on a pilot in Fast Fourier Transform (FFT)-processed data. The data compensation is achieved according to the estimated channels.
The decoder 230 operates according to types of the CTC decoder and the CC decoder. With use of the decoder 230, data error occurring during data transmission is corrected.
The MAP decoder 250 processes FCH and DL-MAP in the frame format defined in 802.16e, shown in FIG. 1. By processing the FCH and the DL-MAP by means of the MAP decoder 250, a Wibro modem of the receiver extracts normal data.
Generally, a structure of an 802.16e-based Wibro modem is roughly divided into a synchronization unit, an Rx data processing unit including the CTC and CC decoders, and a Tx data processing unit including the CTC and CC encoders.
Shown in FIG. 2 is a simple structure realized based on the 802.16e standard, and the use of this structure may have the following problems.
Several data bursts can be carried on one frame, and in the structure of starting data processing after one data burst is fully transmitted, when data is transmitted long along the time axis, the data rate may decrease considerably. In the structure of channel-estimating only the corresponding data after one data is fully transmitted, channel estimation performance degrades, and in the mixed structure of PUSC, FUSC and reuse in the frame, processing of several data bursts increases the complexity. In addition, as data processing is performed after one data burst is fully transmitted, a large number of decoders need to be used to acquire a necessary data rate.
The Wibro modem can have a unique data processing structure according to its manufacturer, and there is a need for efficient block design taking data processing speed and efficiency into account.